(a) The Field of the Invention
The invention is concerned with the art of retro-reflectors for providing nighttime visibility to traffic markings, more particularly but not exclusively to markings laid or formed on road surfaces, such as traffic lane dividing lines, as well as other either vertically or horizontally located signs and markings.
More particularly, this invention is concerned with retro-reflecting assemblies comprising a transparent main globular body more conventionally spheroidal (such main body will be hereinbelow and in the appended claims termed "globule", for simplicity sake, irrespectively of its actual geometry), having a uncoated first surface portion positioned for light impingement, and a plurality of light beams focusing and reflective means, generally a monolayer of transparent microspheres externally coated by a metallic reflective coating, at a second surface portion opposite to said first uncoated portion, for focusing and reflecting light rays which have passed through and been refracted within said globule, so that the impinging light will be reflected outside the globule through said first uncoated surface portion along a path essentially coinciding with that of its impingement on said uncoated portion.
(b) The prior art
This art is a well known and well worked one, and a wide patent literature is available thereon. An analysis about the structure and the optics of retro-reflecting assemblies of the kind referred to above and including each a spherical glass globule has been set forth in the British Patent Specification No. 1,343,196 of same Applicant. An advantageous method for forming a monolayer of microspheres on the surface of the globule and thus providing the assembly has been at its turn set forth in the British Patent Specification No. 1,415,792 also of same Applicant. A plurality of different structures including transparent and not vitreous globules have been proposed and described for example in a further Applicant's British Patent Specification No. 1,443,618. From the above and other available prior publications other details, such as the materials, the dimensions of the assemblies and of their components, the indexes of refraction and so on, have been taught and, therefore, any further discussion about this art is believed to be not necessary.
It is therefore an object of this invention to provide a new and advantageous method for the manufacture of retro-reflecting systems of the type referred to above, in particular of the globules, thereof. Anothr object of this invention is to take advantage of such new method for the manufacture of transparent globules having a new geometry and adapted for the manufacture retro-reflecting assemblies or systems of surprisingly high optical efficiency, long service life-time under severe traffic wear and other advantages which will become apparent as this description proceeds. A further object of this invention is to provide a method for the manufacture of said highly efficient assemblies and systems, and including steps for assembling same in an economical and highly productive manner. A still other object of this invention is to provide a highly efficient retro-reflecting assembly which is characterized by a new combination and arrangement of a particular asymmetrical transparent globule and of a particularly arranged monolayer of focalizing and reflective microspheres.